Author

Yasser Shaban

Defense Date

5-5-2008

Graduation Date

2008

Availability

Immediate Access

Submission Type

dissertation

Degree Name

PhD

Department

Chemistry and Biochemistry

School

Bayer School of Natural and Environmental Sciences

Committee Chair

Shahed U. M. Khan

Committee Member

Bruce Beaver

Committee Member

Julian Talbot

Keywords

Water splitting, Photoelectrochemical cell, Solar hydrogen, Carbon modified TiO2, Carbon modified iron oxide, Self driven PEC for water splitting

Abstract

My Ph.D. Dissertation describes (1) optimization of the synthesis of carbon modified (CM)-n-TiO2, (CM)-n-Fe2O3, and (CM)-p-WO3 semiconductors for efficient photochemical splitting of water, and (2) development of various configurations for self driven photosplitting of water. (1) Thermal flame oxidation was utilized to synthesize carbon modified photocatalysts. The synthesis was carried out by using custom designed large area flame under controlled natural gas and oxygen flows. The carbon modification was achieved by incorporation of carbon into n-TiO2, n-Fe2O3, and p-WO3 structures during thermal flame oxidation. The photoresponses of these films were measured for water splitting reaction under white light illumination from xenon lamp, solar simulator and sunlight, each with intensity of 100 mW cm-2 (1 sun). Optimization of visible light active carbon modified (CM)-n-TiO2 photoelectrons was the first goal pursued in this work. The photoresopnse of carbon modified n-type titanium oxide (CM-n-TiO2) was optimized with respect to several parameters, including Ti metal thickness, flame temperature, oxidation time, Ti metal surface grooving, and combination of spray pyrolysis and thermal flame oxidation methods. Research showed maximum photoconversion efficiencies for water splitting of 9.08% and 11.31% at the optimized flat and grooved CM-n-TiO2 samples synthesized by thermal flame oxidation, respectively. CM-n-TiO2 synthesized by the combination of spray pyrolysis and thermal flame oxidation showed the highest photoconversion efficiency of 14.04% under xenon photoconversion efficiencies of 5.63%, 7.62% and 13.79%, respectively. Carbon modified tungsten oxide (CM-p-WO3) photoelectrodes synthesized by thermal oxidation of tungsten metal sheets exhibited p-type photoresponse with a maximum photoconversion efficiency of 2.16% under xenon lamp illumination. The maximum photoconversion efficiency for water splitting improved significantly from 3.61% for oven made n-Fe2O3 to 6.5% for CM-n-Fe2O3 synthesized by thermal flame oxidation process. (2) Carbon modified (CM)-n-TiO2 was coupled with a p-type semiconductors, p-GaInP2 and CM-p-WO3, in a single compartment PEC, to photosplit water efficiently without the need of any external bias potential. Self-driven solar to hydrogen production efficiencies of 13.03% and 0.5% were obtained for CM-n-TiO2 / p-FaInP2 and CM-n-TiO2 / CM-p-WO3, respectively.

Format

PDF

Language

English

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